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Recently a new vulnerability in Jackson, a popular Java library used for parsing JSON, was published and assigned CVE-2017-7525 and later extended with CVE-2017-15095.

The Jackson-databind package allows programmers to construct Java objects out of JSON documents, and as we have seen in other cases when unserializing untrusted user input and constructing an object out of it may lead to serious consequences like remote code execution.

The Jackson-databind package developers mitigated the vulnerability by creating and maintaining a blacklist of class names that may allow attackers to achieve remote code execution.

For every JSON being unserialized by Jackson-databind the constructed object class name is being checked against this list.

Figure 1: Blacklisted classes as seen in the Jackson-databind source code.

Figure 2: Each JSON that is being unserialized is checked against the blacklisted classes.

The Jackson liberary is also being used in the Apache Struts 2 framework and therefore a security bulletin regarding this vulnerability was published (S2-055).

Mitigating the vulnerability with BIG-IP ASM

ASM users are encouraged to add the following user defined attack signatures to detect exploitation attempts for this vulnerability: